use std::{
    fmt::{Debug, Display},
    num::NonZeroUsize,
    path::Path,
    process::Output,
    time::{Duration, Instant, SystemTime},
};

use color_eyre::{
    eyre::{bail, Context},
    Result,
};
use futures::StreamExt;
use tokio::process::Command;
use tracing::{debug, error, info};

use crate::{
    db::{BuildMode, Db, FullBuildInfo, Status},
    nightlies::Nightlies,
};

struct CustomBuildFlags {
    target: &'static str,
    flags: &'static [&'static str],
}

const CUSTOM_CORE_FLAGS: &[CustomBuildFlags] = &[
    CustomBuildFlags {
        target: "avr-none",
        flags: &["-Ctarget-cpu=atmega328p"],
    },
    CustomBuildFlags {
        target: "amdgcn-amd-amdhsa",
        flags: &["-Ctarget-cpu=gfx1100"],
    },
];

pub struct Toolchain(String);
impl Toolchain {
    pub fn from_nightly(nightly: &str) -> Self {
        Self(format!("nightly-{nightly}"))
    }
}
impl Debug for Toolchain {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0)
    }
}
impl Display for Toolchain {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0)
    }
}

pub async fn background_builder(db: Db) -> Result<()> {
    if concurrent_jobs() == 0 {
        info!("Suspending background thread since DOES_IT_BUILD_PARALLEL_JOBS=0");
        loop {
            tokio::time::sleep(Duration::from_secs(3600)).await;
        }
    }

    loop {
        if let Err(err) = background_builder_inner(&db).await {
            error!(
                ?err,
                "error in background builder, waiting for an hour before retrying: {err}"
            );
            tokio::time::sleep(Duration::from_secs(3600)).await;
        }
    }
}

async fn background_builder_inner(db: &Db) -> Result<()> {
    let nightlies = Nightlies::fetch().await.wrap_err("fetching nightlies")?;
    let already_finished = db
        .finished_nightlies()
        .await
        .wrap_err("fetching finished nightlies")?;

    let next = nightlies.select_latest_to_build(&already_finished);
    match next {
        Some((nightly, mode)) => {
            info!(%nightly, %mode, "Building next nightly");
            let result = build_every_target_for_toolchain(db, &nightly, mode)
                .await
                .wrap_err_with(|| format!("building targets for toolchain {nightly}"));
            if let Err(err) = result {
                error!(%nightly, %mode, ?err, "Failed to build nightly");
                db.finish_nightly_as_broken(&nightly, mode, &format!("{err:?}"))
                    .await
                    .wrap_err("marking nightly as broken")?;
            }
        }
        None => {
            info!("No new nightly, waiting for an hour to try again");
            tokio::time::sleep(Duration::from_secs(60 * 60)).await;
        }
    }
    Ok(())
}

async fn targets_for_toolchain(toolchain: &Toolchain) -> Result<Vec<String>> {
    let output = Command::new("rustc")
        .arg(format!("+{toolchain}"))
        .arg("--print")
        .arg("target-list")
        .output()
        .await
        .wrap_err("failed to spawn rustc")?;
    if !output.status.success() {
        bail!(
            "failed to get target-list from rustc: {:?}",
            String::from_utf8(output.stderr)
        );
    }

    Ok(String::from_utf8(output.stdout)
        .wrap_err("rustc target-list is invalid UTF-8")?
        .split_whitespace()
        .map(ToOwned::to_owned)
        .collect())
}

#[tracing::instrument]
async fn install_toolchain(toolchain: &Toolchain, mode: BuildMode) -> Result<()> {
    info!(%toolchain, "Installing toolchain");

    let result = Command::new("rustup")
        .arg("toolchain")
        .arg("install")
        .arg(&toolchain.0)
        .arg("--profile")
        .arg("minimal")
        .output()
        .await
        .wrap_err("failed to spawn rustup")?;
    if !result.status.success() {
        bail!("rustup failed: {:?}", String::from_utf8(result.stderr));
    }
    let result = Command::new("rustup")
        .arg("component")
        .arg("add")
        .arg("rust-src")
        .arg("--toolchain")
        .arg(&toolchain.0)
        .output()
        .await
        .wrap_err("failed to spawn rustup")?;
    if !result.status.success() {
        bail!("rustup failed: {:?}", String::from_utf8(result.stderr));
    }

    Ok(())
}

#[tracing::instrument]
async fn uninstall_toolchain(toolchain: &Toolchain) -> Result<()> {
    info!(%toolchain, "Uninstalling toolchain");

    let result = Command::new("rustup")
        .arg("toolchain")
        .arg("remove")
        .arg(&toolchain.0)
        .output()
        .await
        .wrap_err("failed to spawn rustup")?;
    if !result.status.success() {
        bail!(
            "rustup toolchain remove failed: {:?}",
            String::from_utf8(result.stderr)
        );
    }
    Ok(())
}

pub async fn build_every_target_for_toolchain(
    db: &Db,
    nightly: &str,
    mode: BuildMode,
) -> Result<()> {
    if db.is_nightly_finished(nightly, mode).await? {
        debug!("Nightly is already finished, not trying again");
        return Ok(());
    }

    let toolchain = Toolchain::from_nightly(nightly);
    install_toolchain(&toolchain, mode).await?;

    let targets = targets_for_toolchain(&toolchain)
        .await
        .wrap_err("failed to get targets")?;

    let results = futures::stream::iter(
        targets
            .iter()
            .map(|target| build_single_target(db, nightly, target, mode)),
    )
    .buffer_unordered(concurrent_jobs())
    .collect::<Vec<Result<()>>>()
    .await;
    for result in results {
        result?;
    }

    for target in targets {
        build_single_target(db, nightly, &target, mode)
            .await
            .wrap_err_with(|| format!("building target {target} for toolchain {toolchain}"))?;
    }

    // Mark it as finished, so we never have to build it again.
    db.finish_nightly(nightly, mode).await?;

    uninstall_toolchain(&toolchain).await?;

    Ok(())
}

#[tracing::instrument(skip(db))]
async fn build_single_target(db: &Db, nightly: &str, target: &str, mode: BuildMode) -> Result<()> {
    let existing = db
        .build_status_full(nightly, target, mode)
        .await
        .wrap_err("getting existing build")?;
    if existing.is_some() {
        debug!("Build already exists");
        return Ok(());
    }

    info!("Building target");

    let tmpdir = tempfile::tempdir().wrap_err("creating temporary directory")?;

    let start_time = Instant::now();

    let result = build_target(tmpdir.path(), &Toolchain::from_nightly(nightly), target)
        .await
        .wrap_err("running build")?;

    db.insert(FullBuildInfo {
        nightly: nightly.into(),
        target: target.into(),
        status: result.status,
        stderr: result.stderr,
        mode,
        rustflags: result.rustflags,
        build_date: Some(
            SystemTime::now()
                .duration_since(SystemTime::UNIX_EPOCH)
                .unwrap()
                .as_millis()
                .try_into()
                .unwrap(),
        ),
        does_it_build_version: Some(crate::VERSION_SHORT.into()),
        build_duration_ms: Some(start_time.elapsed().as_millis().try_into().unwrap()),
    })
    .await?;

    Ok(())
}

struct BuildResult {
    status: Status,
    stderr: String,
    rustflags: Option<String>,
}

/// Build a target core in a temporary directory and see whether it passes or not.
async fn build_target(tmpdir: &Path, toolchain: &Toolchain, target: &str) -> Result<BuildResult> {
    let mut rustflags = None;

    let init = Command::new("cargo")
        .arg(format!("+{toolchain}"))
        .args([
            "init",
            "--lib",
            "--name",
            "target-test",
            "--edition",
            "2015",
        ])
        .current_dir(tmpdir)
        .output()
        .await
        .wrap_err("spawning cargo init")?;
    if !init.status.success() {
        bail!("init failed: {}", String::from_utf8(init.stderr)?);
    }

    let librs = tmpdir.join("src").join("lib.rs");
    std::fs::write(&librs, "#![no_std]\n")
        .wrap_err_with(|| format!("writing to {}", librs.display()))?;

    async fn run(
        toolchain: &Toolchain,
        target: &str,
        rustflags: &mut Option<String>,
        tmpdir: &Path,
        build_std: &str,
    ) -> Result<Output> {
        let mut cmd = Command::new("cargo");
        cmd.arg(format!("+{toolchain}"))
            .args(["build", "--release", "-j1"])
            .arg(build_std)
            .args(["--target", target]);

        let extra_flags = CUSTOM_CORE_FLAGS
            .iter()
            .find(|flags| flags.target == target);

        if let Some(extra_flags) = extra_flags {
            let flags = extra_flags.flags.join(" ");
            cmd.env("RUSTFLAGS", &flags);
            *rustflags = Some(flags);
        }

        cmd.current_dir(tmpdir)
            .output()
            .await
            .wrap_err("spawning cargo build")
    }

    let mut output = run(toolchain, target, &mut rustflags, tmpdir, "-Zbuild-std").await?;
    let mut stderr = String::from_utf8(output.stderr).wrap_err("cargo stderr utf8")?;

    let status = if output.status.success() {
        Status::Pass
    // older cargo (before 2024-12-15) is clueless about std support
    } else if stderr.contains("building std is not supported") {
        info!("Retrying build because std is not supported");
        output = run(
            toolchain,
            target,
            &mut rustflags,
            tmpdir,
            "-Zbuild-std=core",
        )
        .await?;
        stderr = String::from_utf8(output.stderr).wrap_err("cargo stderr utf8")?;

        if output.status.success() {
            Status::Pass
        } else {
            Status::Error
        }
    } else {
        Status::Error
    };

    info!("Finished build");

    Ok(BuildResult {
        status,
        stderr,
        rustflags,
    })
}

fn concurrent_jobs() -> usize {
    std::env::var("DOES_IT_BUILD_PARALLEL_JOBS")
        .map(|jobs| jobs.parse().unwrap())
        .unwrap_or_else(|_| {
            std::thread::available_parallelism()
                .unwrap_or(NonZeroUsize::new(2).unwrap())
                .get()
                / 2
        })
}